1. Field of the Invention
The present invention relates to cable interfacing to electronic chassis. More particularly, the present system relates to an electromagnetic and radio-frequency interference (EMI/RFI) cable entry shield for use with personal computers, electronic cabinets and similar structures.
2. Background Art
The present invention overcomes some of the problems inherent in previous approaches to providing cable interface to electronic chassis. One of these techniques is that of cable bulkheading which involves intermediate connectorization in the cable at the point where it passes through the boundary of the electronic chassis or enclosure.
The obvious cost and difficulty of installing such techniques is apparent because of the intermediate connectorization which requires special units designed to inhibit electromagnetic and radio-frequency interference.
Another technique is that of the method of interleaved flanges or the use of a wave guide below cutoff. In this arrangement, two members with a "Z"-shaped cross-section are oriented parallel to each other and sufficiently close so as to form a "torturous path". The opening thus formed permits cables carrying the desired signals to be routed through. Hopefully, this is impenetrable to most unwanted signals associated with externally generated interference except those at high frequency. High frequency, for the present purpose, implies those signals which are a quarter wavelength less than the largest effective dimension of the opening created with the "Z"-shaped cross-section units.
A search of the background art directed to the subject matter of the present invention conducted in the U.S. Patent and Trademark Office disclosed the following U.S. Letters Pat. Nos.:
5,107,071 5,202,536 PA1 5,170,321 5,204,496 PA1 5,194,691 5,665,937
U.S. Pat. No. 5,107,071 discloses a sealing and shielding structure comprising an elastic sealing member and an electromagnetic shielding member provided in a cavity formed between first and second members which have conductive abutting faces. No facility for the introduction or passage of cables through the structure are disclosed.
U.S. Pat. No. 5,170,321 discloses an enclosure system including a conductive cover shield retained in contact with a substrate having a radio frequency (RF) circuit disposed thereon. Again, no facility for passage of cables or conductors through the enclosure to the exterior are disclosed.
U.S. Pat. No. 5,194,691 discloses a device for providing EMI/RFI shielding for a joint in a cabinet structure that includes a compressible, resilient sealing element and a conductive shielding element bonded to the sealing element and positioned so that the shielding element provides a direct electrical contact across the joint. The shielding arrangement is intended for a cabinet designed to particularly utilize the compressible resilient sealing element. It is also intended to minimize paths by which moisture and debris may enter the cabinet interior. No facility for the passage of cables through the cabinet joints or other shielding means are taught.
U.S. Pat. No. 5,202,536 also teaches a seal for blocking propagation of electromagnetic energy through a gap between bodies having conductive surfaces adjacent to the gap. The invention teaches that the gap includes an elongated core element defining a resiliently compressible cross section which can be molded, extruded or otherwise formed. No facility for the passage of cables through the seal is anticipated by this patent.
U.S. Pat. No. 5,204,496 teaches an EMI shielding gasket made of springy electrically conductive material. The gasket includes a pair of generally parallel laterally spaced apart U-shaped channel members each with its channel entrance facing away from the other member. A pair of ends oriented transversely of the U-shaped channel members connect the members together at their end regions. The ends are resiliently deformable to allow the U-shaped channel members to be moved more closely together to facilitate mounting the gasket. The gasket is usually made of a single piece of metal. No facility for inclusion or passage of cables through the gasket area is taught.
U.S. Pat. No. 5,665,937 features a strain relief bulkhead that provides EMI shielding for data cables being inserted into cabinets by means of the inclusion of a conductive vise, slidably mounted on a stationary guide track permanently attached to a bracket made of conductive material to which a conductive cover panel is removably fastened. A screw mechanism is included to provide an impelling motion for the conductive vise. The vise is moved against the data cables compressing the data cables into contact with each other and with the conductive bracket. A cover panel provides some EMI shielding for the data cables. The conductive bracket, the conductive guide track, the conductive vise, and the cover panel are all made of steel in a preferred embodiment.
A thorough review of the above-identified patents has concluded that none are believed to claim, teach, or disclose the particular novel combination of elements and functions set forth in the present invention. Accordingly, it is the object of the present invention to provide an improved cable entry shielding arrangement that permits multiple cables of varying diameters and stiffness to pass through the boundary of an electronic chassis while minimizing the area of cable passage openings. The resultant reduction in cable passage openings is typically significantly smaller than those associated with prior art techniques. This arrangement is highly desirable inasmuch as in high frequency applications large openings are typically highly detrimental to EMI/RFI shielding effectiveness.